© 2004 by European Society of Cardiology
Copyright © 2003, The European Society of Cardiology
Left ventricular isovolumic velocity and duration variables calculated from colour-coded myocardial velocity images in normal individuals
Department of Clinical Physiology, Karolinska Institutet, Huddinge University Hospital, SE-141 86 Stockholm, Sweden
Received 26 August 2003; received in revised form 11 November 2003; accepted after revision 24 November 2003.
britta.lind{at}hs.se
* Corresponding author. Tel.: +46-8-58581716; fax: +46-8-7748082.
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Abstract |
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 Top Abstract 1 Introduction2 Methods3 Results4 DiscussionAcknowledgmentsReferences |
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Aims: To describe the normal myocardial velocity profile during the isovolumic contraction and relaxation period at four different locations within left ventricular base and to establish normal age and gender related isovolumic time and velocity values.
Methods and results: In 49 healthy individuals (26 women/23 men) in age groups 21–49 and 50–76 years, tissue velocity profiles and 2D-data were acquired at high temporal resolution (90–147 frames/s) for a subsequent off-line analysis using software enabling retrieval of myocardial Doppler velocity and 2D/anatomical M-mode information from different cardiac locations during the same cardiac cycle. The obtained velocity curves during the isovolumic contraction and relaxation period were usually biphasic and displayed clear regional differences in their respective positive and negative maximal velocities. Besides some gender related differences, mainly in the duration of the positive and negative velocity wave components during the isovolumic contraction period, a clear age-dependent increase in the duration of the isovolumic relaxation phase and its negative and positive velocity components was observed.
Conclusion: Modern tissue Doppler imaging supplemented by anatomical M-mode images of the mitral and aortic valve movements allows a proper analysis of the rapid isovolumic myocardial movements. The presented normal isovolumic time and velocity values may prove useful for studies of myocardial function.
Keywords: Tissue Doppler echocardiography; Myocardial velocity; Isovolumic contraction; Isovolumic relaxation
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1 Introduction |
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TopAbstract1 Introduction2 Methods3 Results4 DiscussionAcknowledgmentsReferences |
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The adaptation of pulsed Doppler signal to measurements of low velocity movements of myocardial tissue1 followed by the introduction of 2-dimensional (2D) imaging of cardiac velocities as colour-coded maps2 opened new possibilities for the quantification of myocardial motion in terms of time and velocity and thus provided a new tool for the echocardiographic assessment of myocardial function. A continuous refinement of the tissue Doppler imaging technique during the last decade resulted in steadily increasing temporal and spatial resolution making studies of myocardial wall motions more accurate and detailed. Indeed, a good correlation has been found between the alterations in the systolic and diastolic components of the myocardial tissue velocity profile and the impairment of myocardial perfusion and contractility,1,3–7 and ultimately, also the biological quality of the myocardium in terms of percentage of interstitial fibrosis and density of β-adrenergic receptors.8
In addition to the main systolic and diastolic movements, the high temporal and velocity resolution provided by the latest developments in the myocardial velocity imaging technique also allows the quantification of rapid kinetic events during the systolic and diastolic isovolumic periods. These rapid movements comprise components of very short duration and are considered to be involved in the process of pre- and postsystolic ventricular reshaping.7,9–15 The assessment of the isovolumic temporal, velocity and acceleration parameters along with the evaluation of the main systolic and diastolic events appears to increase the ability of detecting ischemic myocardium,4,7,16 providing at the same time new insights into elastic properties and the contractile force of the myocardium.
However, a successful application of the analysis of the isovolumic kinetics in the evaluation of the myocardial function assumes that, firstly, sampling rate ensuring adequate temporal and velocity resolution is established, and secondly, the normal velocity profile during isovolumic contraction and relaxation period is adequately characterized. In one of our previous studies, we reported on the optimal sampling rate required for a proper rendering of myocardial velocity signal.17 The aim of this study was to describe normal isovolumic myocardial velocity profiles extracted from 2D colour-coded myocardial velocity images18,19 sampled at optimal, high sampling rate in four different myocardial segments of the left ventricular base and to establish normal age and gender related isovolumic time and velocity values.
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2 Methods |
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TopAbstract1 Introduction2 Methods3 Results4 DiscussionAcknowledgmentsReferences |
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The study population comprised 49 volunteers divided into two age groups as described in Table 1. All of them were healthy normotensive individuals in sinus rhythm without any history of cardiovascular disease and without any medication. No abnormalities were detected by physical examination, exercise stress test on a bicycle ergometer with a 12-lead standard ECG recorded continuously, or by routine transthoracic echocardiography.
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The study was approved by the ethics committee at Karolinska Institutet, Huddinge University Hospital, Stockholm, Sweden and all subjects gave their informed consent to participate.
2.1 Image acquisition
All studied individuals were examined with echocardiography and tissue Doppler imaging (TVI) using a GE Vingmed System FiVe (Horten, Norway). A standard phased array 2.5 MHz multifrequency transducer was used. All recordings were performed at the end of expiration from apical four chamber (4CH) and two chamber (2CH) view with the subjects in left lateral position. Cine loops of two consecutive heartbeats were acquired in each case with a high temporal resolution (90–147 frames/s, mean 113), i.e. in four cases with 90 frames/s, in 20 cases with 96 frames/s and in 25 cases with sampling frequency > 100 frames/s. The formatted raw data containing both grey scale and TVI information were stored as IQ-data on magneto-optical disk and then transferred to a Macintosh computer for off-line analysis employing the commercially available software Echopac version 6.3.6 (GE Vingmed).
2.2 Tissue Doppler imaging echocardiography (TVI) analysis
The employed Echopac software allows for real-time digital acquisition of TVI data with a subsequent off-line quantification of the TVI profiles at any point in the myocardial location in the stored cine loops. The TVI analysis was performed from an optimal measuring position set at the basal segment of each wall (septum, lateral, inferior and anterior wall) of the left ventricle, depending on image characteristics (Fig. 1A). The true isovolumic contraction period was established in separate experiments by defining off-line in apical five chamber (5CH) view the time point for the closure of the mitral valve and the opening of the aortic valve using anatomical M-mode in 2D grey scale images from two consecutive heartbeats. The true isovolumic relaxation period was defined similarly by aortic closure and mitral valve opening (Fig. 1B and C). Anatomical colour M-mode extracted from TVI and the myocardial tissue velocity profile from the basal septum were recorded for the same heartbeats (Fig. 1D). The grey scale anatomical M-mode images of the mitral and aortic valve and colour anatomical M-mode images and velocity profiles from the basal septum were then organised and synchronised according to ECG signal using Microsoft® Power Point for Windows version 9.0 (Fig. 1). The following variables in the tissue velocity curve were measured (see Fig. 1A).
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TVI-derived myocardial isovolumic contraction period (TVI-IVCTm): A period of time between the zero crossing point for the ascending limb of the positive isovolumic velocity wave and the zero crossing point for the ascending limb of the myocardial tissue velocity curve at the beginning of the systolic ejection. During this period of time the tissue velocity profile usually shows biphasic pattern of motion, i.e. a positive deflection (IVCmpos) followed by a negative wave (IVCmneg) but single-phase movements (positive or negative) may occur as well. In some of these cases, the zero crossing reference points were not available and the beginning and the end of TVI-IVCTm were defined using the anatomical M-mode images of the closure of the mitral and the opening of the aortic valve.
IVCvmpos: Maximal velocity during the positive wave on the tissue velocity curve during myocardial isovolumic contraction period.
IVCtmpos: Duration of the positive wave on the tissue velocity curve during myocardial isovolumic contraction period.
IVCvmneg: Maximal velocity during the negative wave on the tissue velocity curve during myocardial isovolumic contraction period.
IVCtmneg: Duration of the negative wave on the tissue velocity curve during myocardial isovolumic contraction period.
TVI-derived myocardial isovolumic relaxation period (TVI-IVRTm): A period of time between the zero crossing point for the descending limb of the systolic myocardial tissue velocity curve at the end of the systolic ejection and the zero crossing point for the one-phase (ascending or descending) or two-phase tissue velocity curve at the start of the diastolic E-wave. During this period of time the tissue velocity profile usually shows two-phase tissue motion, i.e. a negative deflection (IVRmneg) followed by a positive wave (IVRmpos) but single-phase movements (positive or negative) may occur as well. If the zero crossing reference points could not be established, TVI-IVRTm was defined using the anatomical M-mode images of the aortic closure and the opening of the mitral valve.
IVRvmneg: Maximal velocity during the negative wave on the tissue velocity curve during myocardial isovolumic relaxation period.
IVRtmneg: Duration of the negative wave on the tissue velocity curve during myocardial isovolumic relaxation period.
IVRvmpos: Maximal velocity of the positive wave on the tissue velocity curve during myocardial isovolumic relaxation period.
IVRtmpos: Duration of the positive wave on the tissue velocity curve during myocardial isovolumic relaxation period.
2.3 Statistics
The intra-observer variability for different systolic and diastolic parameters in the tissue velocity profile varied between 5 and 10%, as described earlier.20
All data are presented as mean ± SD. Statistical analysis was performed by one-way analysis of variance. Where the test statistic (F) attained a level of significance corresponding to p<0.05, Scheffé's test was applied to reveal the distribution of differences between variables. Student's t test for unpaired samples was performed as appropriate. The analyses were carried out using Stat View 5.0.1 for Macintosh.
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3 Results |
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TopAbstract1 Introduction2 Methods3 Results4 DiscussionAcknowledgmentsReferences |
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The demographic and 2D echocardiographic data on the studied population are presented in Table 1. As can be seen in the table, the older patients had a greater interventricular septal wall thickness (p<0.01) and posterior wall thickness (p<0.01) than the individuals in the younger age group. The left ventricular end-diastolic diameter was smaller in the older age group (p<0.01).
3.1 Myocardial isovolumic contraction period
The closure of the mitral valve measured by anatomical M-mode occurred at the beginning of a short red colour band indicating a reversal of the negative myocardial velocity direction in the colour anatomical M-mode from the basal septum (Fig. 1C and D). This corresponded to the zero crossing point for ascending limb of the isovolumic positive wave in the tissue velocity profile from the same myocardial location (Fig. 1A, C and D). The opening of the aortic valve measured by anatomical M-mode occurred at the zero crossing point at the beginning of the systolic ejection in the myocardial velocity profile from the basal septum and coincided with the corresponding reversal of the negative myocardial velocity direction in the anatomical colour M-mode from the same location (Fig. 1A, B and D).
The distribution of the myocardial velocities and time intervals during the TVI-derived isovolumic contraction period in different segments of left ventricle is presented in Table 2. Nearly all individuals (47) displayed a positive velocity wave at the beginning of this period in all four myocardial segments. As can be seen in the table, the myocardial movement with the highest positive velocity occurred in the anterior wall, followed by the inferior wall whereas the velocities measured in the lateral and septal wall were significantly lower (p<0.01). Similarly, the duration of the positive velocity wave was longest in the anterior wall and shortest in the septal wall (p<0.01).
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The positive velocity wave was usually followed by the negative wave. The negative velocity wave was, however, generally less frequent than the positive one. Furthermore, its occurrence varied between the myocardial segments, being most frequent in the segments displaying lowest positive velocities and shortest positive wave durations, i.e. in the septal and lateral left ventricular walls (40 and 39 individuals, respectively), whereas it appeared only in 13 individuals in the anterior segment in which the positive velocity wave was highest and lasted longest (see Table 2). Also, the negative velocities were generally lower than the positive ones (p<0.001) and, contrary to what was valid for IVCvmpos, the anterior left ventricular wall displayed the lowest negative myocardial velocity whereas the highest IVCvmneg was found in the lateral and septal segments (p<0.01). In parallel, the duration of the negative myocardial velocity wave was shortest in the anterior wall and longest in the lateral wall (p<0.01) followed by the inferior segment and septal wall. On average, the duration of the negative velocity wave was significantly shorter than the duration of the positive wave (p<0.001). The TVI-IVCTm was somewhat longer in lateral wall than inferior wall (p<0.05).
3.2 Myocardial isovolumic relaxation period
The closure of the aortic valve measured by anatomical M-mode occurred at the beginning of a short blue colour band indicating a transition to the negative myocardial velocity in the anatomical colour M-mode images from the basal septum at the end of the systolic ejection (Fig. 1B and D). This coincided with the zero crossing point for the descending limb of the systolic ejection wave in the tissue velocity profile from the same myocardial location (Fig. 1A, B and D). The opening of the mitral valve measured by anatomical M-mode coincided with the transition to the negative myocardial velocity at the beginning of the diastolic filling in the anatomical colour M-mode images from the basal septum and corresponded to the zero crossing point for one- or two-phase tissue velocity curve at the start of the diastolic E-wave in the myocardial velocity profile from the same location (Fig. 1A, C and D).
Table 3 gives the segmental distribution of the myocardial velocities and time intervals during TVI-derived isovolumic relaxation period. In almost all individuals (47) a negative velocity wave occurred at the beginning of this period in all four myocardial walls. The maximal velocity during this negative myocardial movement did not differ between the four different segments but the duration of the negative velocity wave was significantly shorter in the septal than in the lateral and anterior walls (p<0.01).
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The initial negative myocardial velocity wave was followed in all myocardial segments by a less frequent positive velocity wave. As can be seen in Table 3, the positive velocity wave was found most frequently in the septal segment of the left ventricle (43 individuals) followed by the inferior and anterior wall, the lowest frequency (21 individuals) being observed in the lateral wall. The highest positive myocardial velocity was found in the septal wall (p<0.01 vs. all other segments) whereas the lateral wall displayed the lowest IVRvmpos. Also the duration of the positive myocardial velocity wave was longest in the septal segment whereas the positive wave of the shortest duration appeared in lateral and inferior segments (p<0.01). The average duration of negative and positive velocity wave was equal. TVI-IVRTm was somewhat longer in the septal than in inferior segments (p<0.05).
3.3 Age and gender differences
The distribution of the global myocardial velocities and time intervals related to the myocardial isovolumic phases in women and men in different age groups is presented in Table 4. As can be seen in the table, the global positive and negative myocardial velocity values during TVI-derived isovolumic contraction period did not differ between men and women. Somewhat lower global IVCvmpos was, however, observed in men in the older age group compared to the younger male individuals (p<0.05). The same was valid for the global positive and negative myocardial velocity values during TVI-derived relaxation period, with the exception for the positive velocity in women in the older age group in which the global IVRvmpos was somewhat lower than that in the corresponding age group in men (p<0.05). When the positive and negative velocity values for men and women during respective isovolumic period were combined, no age related differences in positive or negative myocardial velocities were found (see Table 4).
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As indicated in Table 4, the duration of the positive velocity wave during TVI-derived isovolumic contraction period was somewhat shorter in women than in men in the younger age group (p<0.05) but this gender difference disappeared in the older age group and no age related differences appeared when the values of IVCtmpos in men and women were combined in the two age groups. On the other side, the duration of the negative velocity wave was longer in women than in men in the younger age group (p<0.05) and the difference increased in the older individuals (p<0.01). However, no age related differences were found when the values of IVCtmneg in men and women were combined in both age groups. The gender related difference in the age groups disappeared in TVI-IVCTm as it did after the values in men and women had been combined in both age group.
The duration of the negative velocity wave during TVI-derived isovolumic relaxation period did not differ between men and women but was significantly shorter in the younger individuals (p<0.001), the difference being still apparent when the values for IVRtmneg in men and women were combined in both age groups (p<0.001). Similarly, no gender related differences in the duration of the positive velocity wave during this isovolumic period were found. There was a tendency toward longer IVRtmpos in the older age group but the difference attained the level of statistical significance (p<0.01) only in men. When the values for IVRtmpos in men and women were combined in both age groups, IVRtmpos in the older individuals was still significantly longer (p<0.01). In keeping with these findings, TVI-IVRTm was significantly longer in the older age group (p<0.001).
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4 Discussion |
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TopAbstract1 Introduction2 Methods3 Results4 DiscussionAcknowledgmentsReferences |
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An accurate echocardiographic imaging of rapid kinetic myocardial events requires a technique with a high temporal resolution. Not surprisingly then, the isovolumic myocardial movements of high velocity and short duration were quantified first in 1993 when Isaaz and his colleagues14 applied pulsed wave Doppler technique to myocardial tissue motion measurements. Indeed, the pulsed wave Doppler technique provides sampling frequencies high enough to detect the rapid myocardial movements during isovolumic periods. However, on-line recording of pulsed wave Doppler signal precludes the data acquisition from different sampling points during the same heart cycle and the size of pulsed wave sample produces a spectral broadening of the myocardial velocity waveform limiting the accuracy of the velocity measurements. Furthermore, the characteristics of this method low frequency filtering around baseline makes an accurate temporal estimation of the rapid isovolumic movements uncertain. With the 2D colour-coded myocardial velocity imaging technique used in this study, the myocardial tissue velocity data were acquired at a sampling rate varying between 96 and 143 frames/s depending on inter-individual variations in 2D and tissue velocity imaging sector, depth and pulse repetition frequency due to anatomical circumstances and only in four cases a frame rate of 90 frames/s was employed. Hence, the applied sampling rates even if lower than what would theoretically be possible with pulsed Doppler technique, remained in the majority of cases within the sampling frequency range required for an adequate rendering of the myocardial tissue velocity signal.17 The few observations made with lower frame rate (90 frames/s) caused possibly only a negligible underestimation of velocity and overestimation of time variables. Finally, the tissue velocity imaging technique currently used offers a superior spatial resolution and, in any given projection, a possibility to retrieve Doppler velocity information from different myocardial locations on the same cardiac cycle.
The TVI-derived myocardial isovolumic periods evaluated in the present study represent indeed the true isovolumic phases of the cardiac cycle as evidenced by grey scale images of the closure and opening of the mitral and aortic valves, which events coincided with the specific colour bands in the tissue velocity anatomical colour M-mode images and the applied isovolumic delimitation points on the myocardial velocity profile curve. Besides setting the limits for the true isovolumic phases, the chosen reference points have also an advantage of being easy to define since the respective zero crossing points can be identified in the majority of cases. However, in some normal individuals presenting only a negative or positive velocity wave during the isovolumic contraction or relaxation period, the respective zero crossing reference points may not always be available. In these cases, the definition of the respective isovolumic period limits can be accomplished by the identification of the respective valve closure/opening in the anatomical M-mode images of the aortic or mitral valve movements. The same procedure should be applied when defining the isovolumic relaxation period in patients with, for example, postsystolic contraction caused by myocardial ischemia,21 since the closure of the aortic valve at the beginning of this period does not coincide with any zero crossing point. In this context it has to be emphasised that the isovolumic phases defined by the aortic and mitral valve opening and closure represent global cardiac phenomena whereas the corresponding TVI-derived isovolumic periods reflect regional myocardial events. These events coincide well with the true isovolumic phases when measured in the cardiac base but may diverge if measured in more remote regions as, for example, medial and apical sectors of left ventricular myocardium.
Concerning the validity of the present results it should not be forgotten that the mechanical cardiac events precede their hydraulic consequences resulting in a certain delay between myocardial wall motion and opening/closure of the aortic and mitral valves. The time delay caused by such a mechanic–hydraulic coupling did not appear to influence to any significant extent the synchronicity between the aortic and mitral valve motions derived from the anatomical M-mode images and TVI-derived myocardial motion in normal individuals currently studied. However, in cases of cardiac pathology resulting, for example, in an increased filling pressure, the normal mechanic–hydraulic coupling may be disturbed and the opening of the mitral valve may occur at a measurable time period before the zero crossing point terminating the isovolumic relaxation phase. Under such circumstances, the proper definition of this phase should rely on the anatomical M-mode images of the mitral valve movements.
The occurrence of positive and negative components of the myocardial velocity wave during isovolumic phases found in this study accords well with the results reported from previous animal7,21 and human experiments.13,14,22,23 However, the measured maximal positive and negative velocity values and the duration of the respective isovolumic velocity waves differed between the four cardiac walls considered. During the isovolumic contraction period the highest positive velocities and the longest duration were found at the base of the anterior and inferior left ventricular walls whereas the septal and lateral walls displayed the highest negative velocities of long duration. On the other hand, during the isovolumic relaxation period the highest negative velocities and long wave duration were found in the lateral wall whereas the highest positive velocities of long duration were seen in the septal wall, followed by anterior and inferior walls. The differences in the kinetic expression of the isovolumic phases between different left ventricular walls suggest that isovolumic myocardial movements, rather than being a simple coiling–recoiling phenomenon, seem to be components of a more complex and discriminate twisting–untwisting ventricular reshaping process creating the optimal initial conditions for the ventricular ejection and following ventricular filling.
The issue of isovolumic myocardial movements has attracted increasing interest in recent years since changes in direction, velocity and duration of these movements seem to closely follow the occurrence of myocardial ischemia. In early studies with pulsed wave Doppler technique, prolongation of regional isovolumic relaxation time was observed in patients with coronary artery disease25 and an ischemia-induced increase of isovolumic contraction and relaxation velocities was found during graded ischemia in open-chest anaesthetised pigs.4 In recent studies employing TVI technique, a decrease and reversal of myocardial velocity indicating presystolic myocardial lengthening was seen during isovolumic contraction and predominantly positive velocities indicating postsystolic myocardial shortening were observed during isovolumic relaxation in open-chest, anaesthetised dogs subjected to myocardial ischemia.7 The appearance of ischemia-induced marked positive velocity during the isovolumic relaxation period consistent with postsystolic contraction has been also confirmed in patients during angioplasty26,27 and increasing negative isovolumic contraction velocities and tendency toward increased isovolumic relaxation time were observed in this setting as well.27 The overall picture emerging from the available experimental data seems to depict increasingly negative isovolumic contraction velocities together with increasingly positive isovolumic relaxation velocities and increased duration of the isovolumic relaxation phase as markers of myocardial ischemia. Hence, by measuring the isovolumic variables together with peak systolic velocities the capacity of TVI to identify and quantify ischemia-induced myocardial dysfunction may be significantly improved.
The normal values for the velocity and duration of isovolumic myocardial movements reported hitherto come from studies based on pulsed Doppler technique, relying on a limited number of observations and not stratified for both age and gender.12,14,15 The exception is the study of Edner et al.,24 which however, did not, address specifically the issue of isovolumic periods. In the present study, the time and velocities of the rapid myocardial movements during the isovolumic phases were quantified in different sectors of the cardiac base in healthy men and women in two different age groups. The results did not reveal any systematic gender differences in the measured isovolumic variables apart from the somewhat lower maximal positive velocities during the isovolumic relaxation period in older women as compared to age-matched men and somewhat shorter duration of the positive but longer duration of the negative velocities during the isovolumic contraction period in younger women resulting in longer total isovolumic contraction time compared to men in the younger age group. The age differences were clearly more evident and revealed an age-dependent increase in the duration of both the negative and positive velocity waves and, consequently, an increased duration of the entire isovolumic relaxation phase in older individuals. In this respect, the present data are in agreement with the above-mentioned study of Edner et al.24 who found age being the most important factor influencing pulsed wave Doppler derived total isovolumic relaxation time in the basal septal and lateral walls.
Summing up, the present results demonstrate that modern tissue Doppler imaging technique supplemented by anatomical grey scale M-mode images of the mitral and aortic valve movements allows a proper definition of the isovolumic periods and the measurement of the related rapid kinetic events in different myocardial locations on the same cardiac cycle. The high velocity isovolumic myocardial movements are usually biphasic and the differences in their regional expression may reflect a discriminate pre- and postsystolic ventricular reshaping process bringing about the optimal conditions for ventricular ejection and filling. There seem to exist some gender differences in the duration of the maximal positive and negative velocities during the isovolumic contraction and the maximal positive velocity during the isovolumic relaxation in older individuals and there is a clear age-dependent lengthening of the isovolumic relaxation phase and its positive and negative velocity wave components. This ought to be recognized when evaluating myocardial isovolumic data.
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Acknowledgments |
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TopAbstract1 Introduction2 Methods3 Results4 DiscussionAcknowledgmentsReferences |
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Supported by grants from the Swedish Heart-Lung Foundation, Karolinska Institutet and from Stockholm County Council, Public Health and Medical Services Committee, FOUU-council.
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References |
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